Light-driven rheological modulation of solventless polymer networks enabled by precisely architected flexible star polysiloxanes

We report the synthesis and photoresponsivity of precisely designed liquid star-shaped poly(dimethyl siloxane) (PDMS) with anthracene end groups. Owing to the efficient end-linking of the flexible PDMS arms upon the first UV irradiation (<i>λ</i> = 365 nm, UV₃₆₅), the storage modulus (<i>G</i>') increased from 4.7 Pa to 119 kPa (>25 000-fold), and the physical state became a rubbery solid. Subsequent irradiation with UV light at a shorter wavelength (<i>λ</i> = 254 nm, UV₂₅₄) decreased <i>G</i>' toward the photostationary state, and viscoelasticity modulation was achieved between the two photostationary states under solvent-free conditions.